1. Field of the Invention
This invention generally relates to a sprocket. More specifically, the present invention relates to a bicycle sprocket that is configured to be mounted on the rotating drive unit of a bicycle, and that is configured to engage a bicycle-driving chain that is to be wrapped around the external periphery of the bicycle sprocket.
2. Background Information
Bicycling is becoming an increasingly more popular form of recreation as well as a means of transportation. Moreover, bicycling has become a very popular competitive sport for both amateurs and professionals. Whether the bicycle is used for recreation, transportation or competition, the bicycle industry is constantly improving the various components of the bicycle. One component that has been extensively redesigned is the bicycle sprocket.
When a plurality of sprockets are mounted to the gear crank and free hub in order to provide multiple gears, aluminum is used as the material in order to reduce weight.
A bicycle is generally provided with a drive unit or drive train having front and rear sprockets and a chain wrapped around the sprockets. The front gear crank (one example of a rotating drive unit) of the bicycle has one or more front sprockets, while the free hub (one example of a rotating drive unit) of the bicycle has one or more rear sprockets. This type of bicycle sprocket is made of such materials as an aluminum alloy having the designation A2014P under the standard JIS H4000 (category) or iron having the designation SPCC under the standard JIS G3141 (category). When the gear crank or the free hub has a plurality of sprockets in order to provide multiple gears, aluminum is used as the material in order to reduce the weight.
There are also known bicycle sprocket designs that reduce the weight even further by having a sprocket ring part made of an aluminum alloy with sprocket teeth formed thereon, and a fastening part made of a carbon fiber material that is mounted on the internal periphery of the sprocket ring part and fastened to the gear crank (for example, see German Utility Model Publication No. 20218755). In this sprocket, the internal periphery of the sprocket ring part and the fastening part are fastened together by installing metallic crimping pins in semicircular holes formed in the sprocket ring part and the fastening part. Also, a gap is formed between the sprocket ring part and the fastening part to prevent them from deforming due to the weather as a result of using two members. Furthermore, mounting holes with steps are formed in the fastening part of the gear crank. In a sprocket with such a configuration, normally a bolt (one example of a fastening member) is inserted through the mounting holes to fasten the sprocket to a spider arm of the gear crank.
Another known practice to assist gear shifting is to provide the sprocket with pin members for guiding the chain over the sprocket teeth, which are referred to as spikes or spike pins and sub-spikes or sub-spike pins (for example, see Patent Gazette No. 3583385 Specification). The spike pins are fastened by crimping in fastening holes formed at intervals in the sprocket ring part. The sub-spike pins are fastened by crimping in fastening holes formed farther in on the sprocket ring part than the spike pins and farther upstream of the spike pins in the direction of rotation. The spike pins and sub-spike pins protrude from the larger sprocket to the smaller sprocket.
In the conventional bicycle sprocket previously described, loss of the fastening force between the fastening part and the spider arm (rotating drive unit) can occur as a result of deterioration over time in the synthetic resin constituting the fastening part. Also, the fastening part made of a synthetic resin deforms if the bolt is fastened with excessive torque, which may of course result in a loss of the fastening force.
Also, in the conventional bicycle sprocket previously described, both parts are fastened by crimping pins. When both parts are fastened by crimping pins in this manner, backlash is likely to occur between the two parts. Furthermore, in a conventional sprocket, a gap is formed between the two parts to prevent deformation due to the weather. Therefore, rigidity between the sprocket ring part and the fastening part must be ensured only by the crimping pins, and it is difficult to maintain high rigidity. Also, when the sub-spike pins are disposed farther in than the spike pins, it is difficult to firmly fasten the sub-spike pins in place if a situation arises in which the sub-spike pins must be disposed closer to the fastening part.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved bicycle sprocket. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.